Electrochromic materials and displays

ABSTRACT

Dispersions of electrically conductive particles useful for preparing electrically conductive, essentially ionically isolative composite layers having electrically conductive particles dispersed in a polymer matrix. Composite layers can be used in laminates for electrochromic displays where an ionically conductive layer is in contact with electrochromic material. Such displays comprise means for applying an electrical potential across the interface of the ionically conductive layer and the electrochromic material to generate an electrochromic effect at the interface. Electrochromic materials can be provided in the laminates as layers between the ionically conductive layer and the composite layer of electrically conductive particles dispersed in a polymer matrix. Alternatively, the electrochromic material can be incorporated in the conductive particles in the polymer matrix, e.g. as titanium dioxide coated with antimony tin oxide coated with polyaniline dispersed in an light transmitting polymer matrix. The materials of this invention allow for the high speed fabrication of flexible displays, e.g. by printing methods.

This is a division of application Ser. No. 07/994,813 filed Dec. 22,1992.

Disclosed herein are electrochromic materials, useful for fabricatingelectrochromic laminates which are adaptable forelectrochromically-functional image displays.

BACKGROUND OF THE INVENTION

Japanese Patent Kokai 61-185,730 discloses composite films ofelectrochromic materials such as polyviologen which are bonded to thesurface of electrically conductive particles such as tin oxide by usingcyanuric chloride. Electrochromic displays are produced by coating atransparent electrode (e.g. tin oxide) with a mixture of the compositematerial dispersed in a solution containing a polymer complex such as apolyionic complex of a macromolecular viologen with macromolecularsulfonic acid. An aqueous solution of sodium sulfate in contact with thecomposite provides an electrochromic display element. Color changes withthe application of voltage are visible through the transparentelectrode. The element uses an ionically conducting electrochromic layerand requires the use of a transparent electrode to view the colorchange.

Japanese Patent Kokai 59-113,422 discloses a solid electrochromicdisplay comprising a transparent substrate with a transparent electrodecoating, an electrochromic layer, and another electrode. For example, anelectrochromic layer was cast onto a transparent indium tin oxideelectrode from a solution of a tetrathiafulvavene, polymethacrylonitrileand lithium perchlorate (ion-acceptor); the other electrode was vacuumdeposited metal. Response time for various displays was 2-5 seconds andthe cell requires the use of a transparent electrode to view the colorchange.

Japanese Patent Kokai 63-207,856 discloses a macromolecular displaymaterial comprising a composite of a transparent resin such as PVC andan electrically conductive polymer such as polypyrrole or polythiophenecontaining an electrochromic macromolecule such as tungstic acid orsulfonic acid. Such composite materials coated on conductive,tin-oxide-coated glass provide display materials when immersed in anacetonitrile solution. This cell produced marginal color contrast fromgrey to dark blue.

Japanese Patent Kokai 01-107,135 discloses blends of electrochromicviologen derivatives with polymers to provide a polymeric film or sheetthat can be useful in the manufacture of an oxygen sensor. The reducedviologen derivative dispersed in a polymer matrix changes color readilyon contact with oxygen. Reversible color change requires extensivetreatment to reduce the electrochromic material.

European Patent Publication 193,978 discloses a process for the uniformincorporation of powders into polymer layers which are useful inelectrochromic instruments.

U.S. Pat. No. 4,810,067 discloses an electrochromic device in which anelectrochromic layer is positioned between two electrodes. Theelectrochromic layer is positioned between two electrodes and comprisesan organic material which has been polymerized and condensed supportingelectrochromic particles and ion producing particles.

U.S. Pat. No. 4,550,982 discloses an all solid state organicelectrochromic display device which comprises a polymer layer comprisingat least one organic electrochromic material and at least one ionicmaterial.

European Patent Publication 0 403 180 (Cookson Group, PLC) disclosespowdery or granular material coated with inherently conductive polymer,e.g. polyaniline or polypyrrole, for use in an EMI or RFI shieldingmaterial for compounding into polymer.

Nomura et al. in Journal of Macromolecular Science--Chemistry, A26(2&3),pages 593-608 (1989) disclose electrochemical and electrochromicproperties of polymer complex films composed ofpolytetraamethyleneviologen and poly(p-styrenesulfonic acid) containinga conductive powder.

SUMMARY OF THE INVENTION

This invention provides dispersions of electrically conductive particlesuseful for preparing electrically conductive, essentially ionicallyisolative composite layers having electrically conductive particlesdispersed in a polymer matrix. Such composite layers are useful forcomposite coatings on electrodes for electrochemical applications.Alternatively, such composite layers can be used in laminates which areuseful as electrochromic displays where an ionically conductive layer isin contact with electrochromic material. Such displays comprise meansfor applying an electrical potential across the interface of theionically conductive layer and the electrochromic material to generatean electrochromic effect at the interface. Electrochromic materials canbe provided in the laminates as layers between the ionically conductivelayer and the composite layer of electrically conductive particlesdispersed in a polymer matrix or dissolved or dispersed in the ionicallyconductive layer. Alternatively, the electrochromic material can beincorporated in the conductive particles in the polymer matrix. Inpreferred aspects of this invention the polymer matrix and the ionicallyconductive layers transmit visible light to allow visual observation ofelectrochromic effects. The materials of this invention allow for thehigh speed fabrication of flexible displays, e.g. by printing methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 are partial side views of laminates useful as electrochromicdisplays.

FIG. 7 is a view of an electrode pattern for an electrochromic display.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein the term "electrochromic" refers to a material whichchanges color when subjected to an electrochemical potential. Suchelectrochromic materials are known in the art and include polyaniline,polypyrrole, polythiophene, nickel oxide, polyvinylferrocene,polyviologen, tungsten oxide, iridium oxide, molybdenum oxide andPrussian blue (ferricferrocyanide).

As used herein the term "electrically conductive" refers to a materialwhich conducts electricity including metals such as copper, nickel andaluminum, metal oxides such as tin oxide, indium-doped tin oxide (ITO)and antimony-doped tin oxide (ATO), metal flake in a polymer or resinsuch as silver flake ink, carbon such as graphite or lampblack, andconductive polymers such as polyaniline and polypyrrole. Suchelectrically conductive materials are useful as electrodes inelectrochromic displays. When electrically conductive materials are usedas electrodes, e.g. in displays or other devices, electrochromicmaterials in contact with conductors, such as metals, can beelectrochemically active, e.g. polyaniline can oxidize copperelectrodes. Thus, where extended life is desired, an electricallyconductive material should be selected to minimize electrochemicalinstability arising from contact with electrochromic materials andelectrolyte.

This invention provides dispersions of electrically conductive particlesin (i) a melt processable polymer, (ii) polymerizable monomer oroligomer, or (iii) a liquid containing dissolved or dispersed meltprocessable polymer, polymerizable monomer or oligomer. The electricallyconductive particles consist of (a) an electrically conductive corecoated with an electrochromic material, (b) an electrochromic materialcore and an electrically conductive coating, (c) electrically conductiveelectrochromic material, (d) agglomerations of electrochromic materialand electrically conductive material or (e) electrically conductivematerial. Dispersions of electrically conductive particles, preferablyelectrochromic particles, in a melt processable polymer matrix areuseful for providing thermoplastic composite films. Dispersions ofelectrically conductive particles, preferably electrochromic particlesin polymerizable monomer or oligomer, are useful for casting films of athermoset or crosslinked polymer matrix having electrically conductiveparticles dispersed therein. Dispersions of electrically conductiveparticles in a liquid containing dissolved or dispersed melt processablepolymer, polymerizable monomer or oligomer are useful as inks forprinting patterns of composite having electrically conductive particlesdispersed in a polymer matrix. When the dispersed particles compriseelectrochromic material, such composite films can be used in laminates,e.g. with electrodes printed on one side and an ionically conductivelayer applied to the other, to provide electrochromic displays.Alternatively, electrochromic material can be applied as a separatelayer in the laminate between the composite layer and the ionicallyconductive layer or the electrochromic material can be dissolved ordispersed in the ionically conductive layer.

A preferred aspect of this invention provides inks, adaptable to avariety of printing methods, comprising an emulsion or solution ofpolymer having electrically conductive, preferably also electrochromic,particles dispersed therein. Preferred particles are (a) particlescomprising electrically conductive material, e.g. titanium dioxideparticles coated with electrically conductive ITO or ATO (b) particlescomprising electrically conductive material, such as metal, metal oxideor carbon, coated with an electrochromic material, e.g. titanium dioxideparticles coated with electrically conductive ITO or ATO which is coatedwith electrochromic polyaniline, (c) particles comprising electrochromicmaterial at least partially coated with an electrically conductivematerial, e.g. polyaniline coated with ITO, (d) particles ofelectrically conductive electrochromic material, e.g. polyaniline, or(e) agglomerations of electrochromic material and electricallyconductive material, e.g. agglomerated particles of polyaniline and ITO.

In the laminates of this invention the electrically conductive particlesare provided in a composite with a polymer matrix. In the case of visualdisplays it is generally preferred that the polymer matrix transmitvisible light, i.e. be transparent or translucent to the visible lightspectrum, more preferably be optically clear. The particles can bedispersed in the polymer by a variety of methods. For instance,particles can be dispersed in molten polymer or in solutions of polymer,e.g. toluene solutions of polybutadiene or aqueous emulsions ofpolyvinyl chloride, by homogenization blending. While the polymer can bethermoset, thermoplastic or elastomeric, in many cases it is preferredthat the polymer be optically transparent or translucent, morepreferably optically clear, thermoplastic polymer. Useful thermoplasticpolymers include polystyrene, polyacrylates, polymethacrylates such aspolymethylmethacrylate, polyurethanes, polyolefins such as high or lowdensity polyethylene, linear low density polyethylene and polypropylene,polyesters such as polyethylene terephthalate (PET), polyamides such asnylon-6 and nylon-6,6, polycarbonate, polyvinylchloride (PVC),polyvinylacetal such as polyvinylbutyral, polyvinyl esters such aspolyvinylacetate, polyvinyl alcohol, copolymers such as ethylenevinylacetate copolymer, styrene-acrylonitrile copolymer and styrenemaleic anhydride copolymer, graft copolymers such asacrylonitrile-butadiene-styrene graft polymer commonly known as ABS, andblends thereof. Useful thermoset polymers include epoxy resins,polyester resins, phenol formaldehyde reins and bismaleimide reins.Useful elastomers include acrylic rubber such as polybutylacrylate,olefin rubber such as polybutadiene, ethylene-propylene diene monomerrubber commonly known as EPDM rubber, ethylene-propylene rubber commonlyknown as EP rubber, styrene butadiene rubber and nitrile rubber, andthermoplastic elastomers such as styrene-butadiene block copolymers andblends of polypropylene and EPDM. The above polymers and other polymersuseful in this invention are chosen for use in this invention becausethey do not conduct ions. It is not known whether all of theabove-described polymers absolutely do not transmit ions, e.g. at somede minimus level. In this regard it is expected that there is athreshold ion transmission level that can be tolerated. Regardless theabove polymers and other useful un-named polymers are characterized asessentially ionically isolative. The polymer melt or solution containingdispersed electroconductive particles can be applied as a coating byconventional and well-known methods. Preferably, the polymer is appliedas a thin coating, e.g. about 1-25 micrometer thick, which forms apolymeric film, e.g. on solidification of the melt or evaporation ofsolvent. The polymeric film is disposed as a polymer matrix havingdispersed therein electroconductive particles at sufficiently highdensity as to provide a moderate electrical resistance, e.g. on theorder of 100 ohms to 1,000 ohms, so that the composite polymer layer iselectrically conductive.

In the laminates of this invention a composite polymeric film is appliedover one or more electrodes, e.g. an electrode pattern of metal, metaloxide, carbon, intrinsically conductive polymer or polymer compositehaving an electrical resistance substantially lower than the electricalresistance of the composite material of dispersed particles in a polymermatrix. When the composite polymer material is electrochromic, thematerial can be applied in a pattern covering the electrodes or in anoccluding layer over the electrode pattern area. In another aspect ofthis invention, when the composite polymer material does not containelectrochromic material, laminates can be provided by applying one ormore layers of electrochromic material on the composite polymer layer,e.g. over the entire composite area or in register over the electrodepattern. Where the composite layer has an electrical conductivity lessthan the conductivity of the overlying ionically conductive layer,electrodes can be applied in a side-by-side manner on the same of thecomposite layer opposite the ionically conductive layer. Alternatively,electrodes can be applied to laminates in a sandwich like fashion, withone electrodes at one potential on one side of the laminate in contactwith the composite layer and transparent electrodes, e.g. of metal oxidesuch as ITO, of a different potential applied to the other side of thelaminate in contact with the ionically conductive layer.

In the laminates and electrochromic displays of this invention ionicallyconductive layers comprise aqueous or organic solvent-containingpolymeric gel. Such ionically conductive layers are in contact withelectrochromic material to provide an interface for generatingelectrochromic effects. Such ionically conductive layer preferablycomprises an aqueous polymeric gel which can contain a humectant orhygroscopic filler. Useful hygroscopic material includes deliquescentmaterial such as lithium chloride, calcium chloride, glycerine, sodiumdihydrogen phosphate or lithium trifluoromethylsulfonate. A preferredaqueous polymeric gel is polyacrylamidomethylpropanesulfonate, known asPOLYAMPS. In certain of the laminates of this invention the ionicallyconductive layer is coated with a non-conducting, preferably lighttransmitting, barrier layer to maintain the gel like character of thelayer. In other cases the ionically conductive layer is optionallycoated with a light transmitting electrode material, e.g. ITO, in apattern or a film.

In the laminates of this invention described above, the interfacebetween the ionically conductive layer and the electrochromic materialis electrochromically activatable when an electric potential is appliedacross said interface. For instance, the electrical resistance of a thinelectrochromic composite layer is sufficiently high that side by sideelectrodes at a differential voltage can be used under the laminatewithout excessive short circuit current between side by side electrodes.That is, the path of least resistance is from one electrode through theelectrochromic composite layer to an ionically conductive gel layer backthrough the electrochromic composite layer to the other electrode. Theelectrochromic effect is observed at the interface between theelectrochromic composite layer and the ionically conductive layer. Atransfer of electrons to the electrochromic particles requires iontransfer to or from the electrochromic material. Because the matrixpolymer of the composite is essentially ionically non-conductive, iontransfer from the ionically conductive layer to electrochromic materialoccurs at the interface between layers and not substantially at theunderlying electrode structure. The mobility of ions to or fromelectrochromic material at the interface allows electron transfer to themobile ion-receptive electrochromic material at the interface. A changein the electron oxidation state of the electrochromic material resultsin a change in color in the material at the interface. By arrangingelectrode in patterns, a variety of images can be generated by theelectrochromic effect. In certain preferred aspects of this inventionthe electrochromic image is erasable by removal or reversal of theelectrical potential that created said image.

In view of the above description one aspect of this invention provideselectrochromic displays comprising:

(a) at least one electrode, e.g. applied to a nonconductive flexiblesubstrate, and (b) an electrically conductive, essentially ionicallyisolative composite layer in contact with said electrode, where thelayer comprises a dispersion of electrochromic particles in a visiblelight transmitting polymer matrix, and (c) a visible light transmitting,ionically conductive layer coated onto the composite layer. Theinterface between the layers is electrochromically activatable when anelectric potential is applied across the interface.

With reference to FIGS. 1-6 there is illustrated a variety of laminateelectrochromic displays made possible by this invention. These laminatescomprise a substrate A, e.g. a nonconductive layer of polyethyleneterephthalate (PET) film, coated with a conductive layer B of one ormore electrodes, e.g. metal, metal oxide, conductive polymer or carbon.Layer C₁ is an electrically conductive, essentially ionically isolative,electrochromic composite layer comprising a dispersion of electricallyconductive, electrochromic particles dispersed in a polymer matrix, e.g.titanium dioxide particles coated with ATO and polyaniline dispersed ina rubber matrix. Layer C₂ is an electrically conductive, essentiallyionically isolative composite layer comprising a dispersion ofelectrically conductive, (non-electrochromic) particles dispersed in apolymer matrix, e.g. titanium dioxide particles coated with ATOdispersed in a rubber matrix. Layer C₃ is a layer of electrochromicmaterial, e.g. polyaniline. Layer D is an ionically conductive layer,e.g. POLYAMPS gel. Transparent conductor layer E, e.g. an ITO coatedfilm, can serve as an electrode and transparent, insulating layer F,e.g. a PET film can serve as a provide to loss of electrolyte from theconductive layer. With reference to FIG. 1, an electric potentialbetween electrodes B and E will create an electrochromic effect at theinterface of layers C₁ and D. FIG. 2 illustrates a display havingside-by-side electrodes B, on substrate A. Because the conductivity ofthe electrochromic composite layer C₁ is lower than the conductivity ofthe ionically conductive layer D, current will preferentially flow fromone electrode through the electrochromic composite layer to theionically conductive layer to the area above the next electrode where itwill pass in a reverse direction through the electrochromic layer to thesecond electrode. Where the electrochromic material changes color withthe loss of an anion, the electrochromic effect will be visible over oneelectrode. Where the electrochromic material changes color with both thegain and loss of an anion, e.g. as in the case of polyaniline,electrochromic effects will be visible over both electrodes.

FIGS. 3, 4, 5 and 6 illustrate bipolar electrodes. In FIGS. 3 and 4, anelectrical potential difference across the outer electrodes willgenerate bipolar potential differences at different halves of theintermediate electrodes so as to create opposite electrochromic effectsin the interface of layers C₁ and D over the bipolar charged ends ofeach intermediate electrode. In FIG. 5, the opposite electrochromiceffects are created at the interface between layers C₁ and D under theedges of the segmented electrolyte layer D. In FIG. 6, the oppositeelectrochromic effects are created at edges of segmented sectionscreating the interface of electrochromic layer C₃ and the ionicallyconductive layer D.

A preferred application for non-electrochromic composites, e.g.ATO/titanium dioxide in a polymer matrix, is for electrode coatings forelectrochemical processing. For instance, an electrode comprising acopper substrate coated with a non-electrochromic composite of thisinvention exhibits a resistance to electrochemical redox attack similarto the electrochemical redox resistance of a platinum electrode, e.g.for voltammetric applications.

While the following examples illustrate the use of various materials inembodiments of the electrochromic inks, composites, laminates anddisplays and methods of this invention, it should be clear from thevariety of species discussed herein that there is no intention of solimiting the scope of the invention. On the contrary, it is intendedthat the breadth of the invention illustrated by reference to thefollowing examples will applies to other embodiments which would beobvious to practitioners in the electrochromic arts.

EXAMPLE 1

This example illustrates embodiments of this invention employingpolyaniline as an electrochromic material. Electrochromic particles wereprepared using ATO coated titanium oxide particles (0.2) micrometer indiameter obtained from Mitsubishi Materials company Ltd as W-1conducting particles. 10 g of the conducting particles were dispersed in30 ml dilute hydrochloric acid (about 4%), in an ice bath, followed bythe addition of 1 g aniline and 1.15 g ammonium persulfate (in 20 mlwater) to initiate polymerization of the aniline on the ATO surface ofthe particles. After polymerization the solution was filtered, washedand dried providing pale green electrochromic particles, i.e. particleswith an electrically conductive core (ATO on titanium dioxide) coatedwith an electrochromic material (polyaniline). 3 g of the electrochromicparticles were dispersed with homogenization into a 10 g solution oftoluene containing 3 g styrene-butadiene rubber (SBR) to provide anelectrochromic ink. A multiple electrode pattern comprising silver flakeconductive ink was printed onto a PET substrate. The electrode patternwas coated with a thin film of the electrochromic ink. After theelectrochromic ink was allowed to dry to form a green, electrochromiccomposite polymer film, a layer of ionically conductive gel (i.e.POLYAMPS) was applied. The gel was covered with a second layer of PET.When any two electrodes in the pattern were subjected to a differentialvoltage (e.g. in the range of 0.5 to 3 volts), the electrochromicmaterial at the interface over the more electronegative electrode (thecathode) was reduced, changing the color at the interface over thecathode to a light white color. Simultaneously, the electrochromicmaterial at the interface over the more electropositive electrode (theanode) was oxidized, changing the color at the interface over the anodeto a dark blue color.

EXAMPLE 2

Electrochromic particles were prepared in the manner of Example 1employing polypyrrole in place of polyaniline. The particles wereemployed in electrochromic displays Example 1, the polypyrrole changingreversibly from blue-black at the anode to light grey-brown at thecathode.

EXAMPLE 3

Electrochromic particles were prepared having a tungsten oxideelectrochromic material coating over ATO/titanium dioxide conductingparticles. When used in displays as in Example 1, the normally whitecomposite layer changed reversibly to a blue color at the interface overthe cathode.

EXAMPLE 4

Electrochromic particles were prepared having Prussian Blueelectrochromic material coating over ATO/titanium dioxide conductingparticles; the Prussian Blue material was prepared from a mixture offerric chloride, potassium ferricyanide and potassium chloride in water.When used in displays as in Example 1, the normally light blue compositelayer changed to a white color at the interface over the cathode.

EXAMPLE 5

Electrochromic particles were prepared by coating poly(p-xylylviologen)poly(styrenesulfonate) over ATO/titanium dioxide conducting particles.10 g of conducting particles was mixed with a solution of 1 g of thepolyviologen in a mixture of 24 ml of dioxane and 24 ml of concentratedHCl; the solution was dried to a powder which was ground and mixed at3:1 with SBR (10% in toluene), providing a suspension of electrochromicparticles. The solution coated onto copper electrodes, dried andimmersed in an aqueous, electrolyte solution of sodium sulfate;application of electric potential resulting in electrochromic switchingbetween purple (cathode) and white (anode).

EXAMPLE 6

1.5 g of conductive powder (ATO on titanium dioxide) was dispersed in 5g of a toluene solution containing 10 wt % SBR. A 0.15 mm thick film ofthe dispersion coated on glass exhibited a resistance of about 10 ohmsacross the thickness of the film. A PET film coated with copper wascoated with the dispersion; after drying the dispersion, the laminatewith a conductive composite film was immersed in 80 ml of a solution of1 ml aniline in dilute sulfuric acid. With the application of 1-2 voltsa deep blue layer of polyaniline was coated anodically onto thelaminate, reversal of electrical polarity allowed the color to switchbetween deep blue and a yellow-green.

EXAMPLE 7

The procedure of Example 6 was repeated except the laminate with aconductive composite film was immersed in 80 ml of a solution of 1 mlpyrrole in dilute sodium chloride. A blue-black layer of polypyrrole wascoated anodically onto the laminate, reversal of electrical polarityallowed the color to switch between blue-black and grey-brown.

EXAMPLE 8

With reference to drawings the pattern of FIG. 7 was silk screen printedusing silver ink (Metech 2500 M). The dried pattern was coated with asolution of 7 g toluene, 3 g of SBR having 3 g of dispersed particles ofpolyaniline/ATO/titanium dioxide. The dried composite layer was coatedwith POLYAMPS. A switching potential of ±1.5 volts DC applied to theelectrodes caused alternate blue (anode) or white (cathode) lettering toappear in a light green field.

EXAMPLE 9

The procedure of Example 8 was repeated except the dried pattern wascoated with a toluene solution of SBR having dispersed particles ofpolyviologen-polystyrene sulfonate/ATO/titanium dioxide. A reversiblecolor change pattern was produced.

EXAMPLE 10

2 g of ATO/titanium oxide particles, 1 g of Versicon™ polyaniline(Allied-Signal) and 10 g of a toluene solution of SBR (1 g) washomogenized for one minute. 1.2 g of the homogenized dispersion wasmixed with 1.2 g of a toluene solution of SBR (0.12 g) to provide adispersion of agglomerates of conductive particles and electrochromicparticles in an rubber solution. The dispersion was coated onto a PETfilm with copper electrodes. Application of a reversing 6 volt DCpotential caused the coating over the electrodes to change between greyand blue.

EXAMPLE 11

The procedure of Example 10 was repeated except that conductiveparticles of ATO/titanium dioxide were omitted. The application of a 1.5volt DC electric field produced no discernible electrochromic effect.

EXAMPLE 12

With reference to FIG. 3, a bipolar electrochromic display was producedby coating an electrode layer pattern from silver ink on PET film. Thedried electrodes was coated with an electrochromic ink of a dispersionof polyaniline/ATO/titanium dioxide particles in a toluene solution ofSBR. The dried composite layer was coated with POLYAMPS. The applicationof a 0.4 volt DC electrical potential difference across the outerelectrodes generated bipolar potential differences at different halvesof the intermediate electrodes so as to create blue and light greenelectrochromic effects on the halves of the interface over the centralelectrodes.

EXAMPLE 13

The procedure of Example 10 was essentially repeated except theelectrochromic dispersion was prepared from conductive particles oftungsten oxide/ATO/titanium dioxide dispersed in a toluene solution ofSBR. A reversible electrochromic blue image was displayed with thealternating application of 1.5 volts DC.

EXAMPLE 14

Polyaniline solution was coated onto a PET film and dried to provide aconductive coating with a resistivity of about 100 ohms/square. A thinscratch of the conductive coating was removed to provide two contiguouselectrodes which were coated with an electrochromic ink containingpolyaniline/ATO/titanium dioxide dispersed in a toluene solution of SBR.The ink was dried to provide a composite coating which was coated withPOLYAMPS. The alternating application of 1.5 volts DC to the electrodescaused a color change between dark blue and very pale green (almostwhite).

EXAMPLE 15

The procedure of Example 14 was repeated without the electrochromiccomposite layer; that is, POLYAMPS was coated directed onto thepolyaniline electrodes. The application of 3 volts DC caused the anodeto slowly darken from a blue-green to a deeper blue-green and thecathode to lighten to a yellow-green. There was a long (several minutes)delay for color change on reversal of voltage.

EXAMPLE 16

1 g of polyaniline was mixed with 10 g of a toluene solution of SBR (1g) in a homogenizer for 1 minute. The dispersion was coated overelectrodes printed on a PET film, dried and overcoated with POLYAMPS,providing a black colored laminate. A weak electrochromic effect wasobserved with the application of ±1.5 volts DC; with 3-5 minutes ofapplied voltage slight lightening of the black color would be observedover the cathode, with no change observable over the anode.

3.4 g of the dispersion was blended with 0.24 g of titanium dioxide,providing a dark grey dispersion which was used to prepare a laminatehaving a dark grey color. With the application of 1.5 volts DC thecathode lightened to a yellowish grey and the anode darkened. Withvoltage reversal colors changed in 15-20 seconds.

EXAMPLE 17

An electrochromic solution was prepared by mixing 0.1 g of lithiumbromide in 5 ml of a saturated, aqueous solution of bismuth nitrate. Thesolution was coated onto a laminate comprising a PET film substrate,silver electrodes and a layer of ATO/titanium dioxide dispersed in SBR.With the application of 1.5 volts DC the cathode turned dark grey andslowly faded on removal of the electric field.

EXAMPLE 18

An electrochromic dispersion was prepared by homogenizing 2 g ofpolyaniline/ATO/titanium dioxide particles in an emulsion of 2.4 gpolyvinylchloride (PVC) and 12 g water. The viscous emulsion was coatedonto silver electrodes on a PET film, dried and coated with POLYAMPS,providing a laminate that exhibited color change with the application of1.5 volts DC.

EXAMPLE 19

The procedure of Example 1 was essentially repeated except theelectrodes on the PET film were (a) silver coated with a carbon (Metech2513) (b) aluminum foil, (c) carbon or (d) polyaniline. Thesilver/carbon and aluminum foil electrodes provided rapid electrochromicdisplay at 1.5 volts DC; the carbon electrodes, at 3 volts DC; and thepolyaniline electrodes, at 10 volts DC.

EXAMPLE 20

An electrochromic dispersion prepared by homogenizing 3 g ofpolyaniline/ATO/titanium dioxide in 10 g of a toluene solution of SBR (3g) was coated over two silver/carbon electrodes on PET film, dried for 2minutes at 110° C., coated with a 10% aqueous solution of POLYAMPS andcovered with a PET film. The electrodes were connected to a functiongenerator supplying ±1.5 volt square waves. At 20 Hertz a flashingelectrochromic color change was clearly visible with lightening of coloras the primary perceived effect. At lower frequencies alternativedarkening to a deep blue could also be perceived. The laminate displayedan electrochromic effect for more than 4 million cycles.

EXAMPLE 21

With reference to FIG. 6, an bipolar electrochromic display wasconstructed by coating two silver electrodes about 40 mm apart on a PETfilm. The area between the electrodes was coated with a layer ofATO/titanium dioxide dispersed in SBR. Three electrochromic areas wereprovided between the electrodes by applying area coatings ofpolyaniline/ATO/titanium dioxide; the electrochromic areas were coatedwith POLYAMPS. Application of 10 volts DC across the silver electrodescaused the edges of the polyaniline-containing areas to exhibit abipolar electrochromic effect--color change was blue toward oneelectrode and white toward the other electrode.

While specific embodiments have been described herein, it should beapparent to those skilled in the art that various modifications thereofcan be made without departing from the true spirit and scope of theinvention. Accordingly, it is intended that the following claims coverall such modifications within the full inventive concept.

What is claimed is:
 1. A method of fabricating flexible electrochromicdisplays comprising an ionically conductive layer on an electrochromiclayer, said method comprising printing an electrode pattern in contactwith an electrically conductive, essentially ionically isolativecomposite layer of electroconductive particles dispersed in a polymermatrix.
 2. An electrochromic display laminate comprising:(a) a substratecoated in one or more areas with a layer of an electrically conductivematerial forming electrode areas on said substrate; (b) an ionicallyisolative layer of an electrically conductive, essentially ionicallyisolative material on said electrode areas; (c) a layer of ionicallyconductive material on said ionically isolative layer;whereinelectrochromic material is present at an interfacial zone between saidionically isolative layer and said ionically conductive layer, saidelectrochromic material being dispersed or dissolved in said ionicallyisolative material, in said ionically conductive material, in both ofsaid ionically isolative and ionically conductive materials or ispresent in a separate layer in said interfacial zone; and wherein saidlaminate has electrode areas adapted to provide an electrical potentialacross said interfacial zone to generate an electrochromic effect atsaid interfacial zone.
 3. A laminate according to claim 2 wherein saidelectrochromic material comprises particles selected from the groupconsisting of:(a) an electrically conductive core coated withelectrochromic material, (b) an electrochromic material core and anelectrically conductive coating, (c) electrically conductiveelectrochromic material, or (d) agglomerations of electrochromicmaterial and electrically conductive material.
 4. A laminate accordingto claim 3 wherein said electrochromic material is selected from thegroup consisting of a polyaniline, a polypyrrole, a polythiophene, apolyvinylferrocene, a polyviologen, tungsten oxide, iridium oxide,molybdenum oxide, nickel oxide and Prussian blue.
 5. A laminateaccording to claim 3 wherein said particles of electrochromic materialare dispersed in the layer of one or more areas of an electricallyconductive, essentially ionically isolative material.
 6. A laminateaccording to claim 5 wherein said layer of one or more areas of anelectrically conductive, essentially ionically isolative materialcomprises said particles of electrochromic material dispersed in atransparent or translucent polymer matrix.
 7. A laminate according toclaim 6 wherein said polymer matrix is an optically transparent ortranslucent clear thermoplastic polymer selected from the groupconsisting of a polystyrene, polyacrylate, polymethacrylate,polyurethane, polyolefin, polyester, polyamide, polycarbonate, polyvinylhalide, polyvinyl acetal, polyvinyl ester, polyvinyl alcohol,styreneacrylonitrile copolymer, acrylonitrile-butadiene-styrene graftcopolymer or blends thereof or a elastomeric polymer selected from agroup consisting of acrylate rubber, butadiene rubber,ethylene-propylene diene monomer rubber, ethylene-propylene rubber,styrene butadiene rubber and nitrile rubber or a thermoplastic elastomercomprising a blend of polypropylene and rubber.
 8. A laminate accordingto claim 3 wherein said layer of ionically conductive material comprisesa polymeric gel containing a hygroscopic material or a humectant.
 9. Alaminate according to claim 8 wherein said hygroscopic material which isa deliquescent material is selected from the group consisting of lithiumbromide, calcium chloride, glycerins, sodium dihydrogen phosphate andlithium trifluoromethylsulfonate.
 10. A laminate according to claim 2wherein said electrodes comprise metal, metal oxide, carbon,intrinsically conducting polymer or polymer filled with conductiveparticles.
 11. A laminate according to claim 2 wherein said electricalpotential is applied by means of two or more electrodes in contact withseparate areas of the layer of electrically conductive, essentiallyionically isolative material and electrically joined by said material;wherein the electrical resistance between said electrodes is lowest in apath running from said electrodes to said ionically isolative materialconnected through said layer of ionically conductive material.
 12. Alaminate according to claim 2 wherein the there is electricalconductivity between said areas of ionically isolative material suchthat the path of lowest electrical resistance between said areas isthrough said layer of ionically conductive material, whereby saidelectrochromic image is erasable by removal of the electrical potentialthat created said image and without external means of short circuitingthe electrodes that created the image.
 13. A laminate according to claim2 further comprising an electrically-conductive, visiblelight-transmitting layer on said layer of ionically conductive material.14. A laminate according to claim 2 wherein said layers are disposed onat least one side of a flexible substrate, whereby said laminate isflexible.